1. Field of the Invention
The present invention relates to a pump and trap for feeding a liquid such as water, fuel, etc. The pump and trap of the present invention is suitable particularly for use in collecting a condensate generated in a steam piping system and feeding this condensate to a boiler or a waste heat recovery system.
2. Description of the Related Art
Condensate generated in a steam piping system in most cases still has a considerable quantity of heat. It therefore has been a widespread practice to provide a condensate recovery system, including a pump for recovering the condensate and feeding it into a boiler or a waste heat recovery system for the purpose of effective utilization of waste heat from the condensate, thus making effective use of this energy.
The pump used in prior art condensate recovery system collects the condensate in a vessel, and then introduces a high-pressure working fluid--such as steam--into the vessel by operating a change-over valve. The pressure of the high-pressure working fluid discharges the condensate from the inside of the vessel. To insure high-efficiency operation of the pump, it is necessary to collect as much condensate as possible within the vessel and to properly switch the change-over valve.
The pump of the prior art, therefore, generally adopts a snap mechanism, provided with a coil spring. in order to insure reliable switching of the change-over valve. A pump which is equipped with a built-in snap mechanism provided with a coil spring is disclosed in U.S. Pat. No. 5,141,405, to Francart.
FIG. 13 is a front view of a snap mechanism used in the prior art pump described in the Francart patent. In the pump disclosed in the Francart patent, the snap mechanism 100 comprises a main arm 101, a first arm 102, and a coil compression spring 103. The main arm 101 is pivotally supported, by a first shaft 106, on a supporting member or frame 105. On the forward end of the main arm 101 is connected a float 108, through a screw member 104 which is fastened to the float 108.
The first arm 102 is connected at one end to the supporting member 105 by the first shaft 106, and therefore to the main arm 101, and at the other end to one end of the coil spring 103 by a third shaft 110, through a spring bracket member 116. The other end of the coil spring 103 is connected to the main arm 101 by a second shaft 112 through a spring bracket member 115. A valve spindle operating rod 111 is connected by a shaft 107 to the center part of the first arm 102. The valve spindle (not shown) and the snapping mechanism 100 are linked to the change-over valve through the valve spindle operating rod 111.
In the prior art pump, accumulation of condensate in the vessel (not shown) causes the float 108 to rise. As the float 108 rises, the spring bracket member 115 side of the coil spring 103 moves upward, thus compressing the coil spring 103. With further rise of the float 108, the coil spring 103 is in line with the first arm 102. The float 108 rises further until an angle between the coil spring 103 and the first arm 102 exceeds 180 degrees. As a result, the coil spring 103 suddenly recovers from compression, and the connecting section (the third shaft 110) between the coil spring 103 and the first arm 102 snaps downward. This movement results in downward movement of the valve spindle operating rod 111 connected to the first arm to thereby suddenly switch the change-over valve (not shown).
The prior art pump has a problem--notwithstanding its simple design and its ability to relatively efficiently pump liquid--that a great deal of buoyancy, or a large float, is needed to obtain a large force for proper switching of the change-over valve. This is because, in a triangle formed by the first shaft 106, the second shaft 112, and the third shaft 110, the distance between the first shaft 106 and the second shaft 112 is longer than that between the first shaft 106 and the third shaft 110. The distance between the first shaft 106 and the second shaft 112 is long, and accordingly the magnification of buoyancy produced by the main arm 101 and transmitted to the first arm 102 is small. Furthermore, since the distance between the first shaft 106 and the third shaft 110 is short, the magnification of buoyancy by the first arm 102 which is transmitted to the valve spindle operating rod 111 is also small.